The present invention pertains to compasses which can be used to find a direction with reference to the magnetic North while at the same time causing as little disturbance as possible in the local magnetic field in the vicinity of this compass.
In the prior art, a direction is determined with reference to the magnetic North by using a conventional type of compass comprising a little magnet mounted on a needle. A graduated dial known as a compass card, fixed to the magnet, is used to find the chosen direction according to the graduations on it.
Although the level of disturbance that an instrument of this type causes in the local magnetic field is low, it is nevertheless troublesome in certain cases. Thus, such disturbance is quite capable of actuating the triggering device of a magnetic mine. Now undersea divers have to use compasses of this type to guide themselves under water, and they therefore run the risk of accidentally triggering magnetic mines of this type, especially when they are engaged in mine-clearing operations.
There are also terrestrial magnetic compasses in the prior art, known as flux gates, comprising a probe fitted with a saturable core located within an exciting coil. The Earth's continuous magnetic field, superimposed on the excitation field induced by the coil, causes an imbalance in the electrical current produced by this excitation field. The measurement of this imbalance can be used to determine the orientation and value of the Earth's continuous magnetic field.